Hitherto, as a spark advance mechanism in an ignition apparatus, a mechanism of the mechanical type which changes the ignition timing by mechanically moving the position of the magnet stator has generally been used. However, the mechanical type spark advance mechanism is complicated and has a slide portion, so that there is a problem of durability.
To eliminate this problem, and electrical spark advance apparatus to electrically change the ignition timing has been proposed. As the simplest electrical spark advance apparatus, an apparatus to merely change the ignition timing in a manner interlocked with the rotational speed of the engine has been known. However, this apparatus has a drawback of starting performance because the ignition timing is delayed for the longest time at the start of the engine (when the engine has the lowest rotational speed).
On the other hand, an electrical spark advance control mechanism to advance the ignition timing only at the start of the engine from the ignition timing in the stationary state has been disclosed in JP-A No. 60-195378. FIG. 1 shows a schematic diagram of such a conventional electrical spark advance control mechanism. FIG. 1 shows a contactless ignition apparatus of the capacitor discharge type which is constituted in a manner such that an output of a capacitor charging coil 1 is rectified via a diode 4 and charges a capacitor 5, and a spark for ignition is generated from a spark plug 7 by a high voltage which is developed in a secondary coil 3b when the charges from capacitor 5 are discharged through a thyristor 6 and a primary coil 3a of an ignition coil 3. According to this type of apparatus, a signal supply circuit section B which supplies an ignition signal to the thyristor 6 can advance the supply timing of the ignition signal from a set timing in accordance with a spark advance signal from a spark advance circuit section S (1) when the engine starts, (2) when the engine temperature is low, or (3) when the engine speed is low.
The above contactless ignition apparatus will now be further described in detail. A pulser coil 2 which operates synchronously with the rotation of the engine is provided. Output pulses of the pulser coil 2 are transmitted through a waveform shaping circuit 11 and supplied as ignition signals to the thyristor 6. Thus, the thyristor 6 is turned on and allows a spark for ignition to be generated from the ignition coil 3. In this case, a rotational speed detecting circuit E is simultaneously made operative by the supply of the output pulses from the pulser coil 2. The rotational speed of the engine is detected from the pulses of the pulser coil 2, thereby making operative a control circuit 15 of the signal supply circuit B. As practically shown in FIG. 2, the control circuit 15 defines the spark advance characteristic so as to change in accordance with the engine speed the ignition position or spark timing to the ignition coil 3 when the engine speed is above a predetermined speed N.sub.2.
Further, a starter switch 16 to drive a starter relay 20 to supply a current to a starter motor 19 is provided.
The operation of the starter switch 16 is detected by a starter operation detecting circuit C. The detecting circuit C has a control function such that the ignition timing is set to the spark advance position when the starter motor 19 operates. Practically speaking, the starter operation detecting circuit C maintains the ignition timing at the spark advance position by extending a set time of a timer (provided in the engine temperature detecting circuit D) by only an operating time T when the engine is cold as shown in FIG. 3 in accordance with the engine temperature detected by the engine temperature detecting circuit D. Thus, the starting performance of the ignition apparatus is improved.
When the engine speed and the ignition timing were simply functionally interlocked in the electrical spark advance control mechanism, the ignition timing was delayed with the longest time at the start of the engine when the engine speed was low, so that there is a problem of starting performance.
On the other hand, in the conventional techniques described in FIGS. 1 to 3, when the engine temperature is low just after the start of the engine, the timer is operated for a predetermined period of time in response to a start signal generated upon actuation of the starter motor 19. For the period of time when the timer is operating, the control circuit 15 of the signal supply circuit B is set to ON, thereby advancing the supply timing of the ignition signal from the set position.
However, in such a case, when the engine speed is increased during the operation of the timer in order to set the engine operating mode into the running mode, the ignition timing just described becomes abnormally early. Therefore, the pressure in the cylinder rises to a value above the allowable limit and in the worst case, there is a fear of trouble such as a hole being formed in the piston. Accordingly, the foregoing conventional ignition apparatus has a problem in that the engine speed must be accelerated only after certainly confirming the elapse of the set time of the timer.
On the other hand, in the case of interlocking the ignition timing with the engine speed, the set rotational speed detected by the speed detecting circuit E cannot be set to a high speed corresponding to a trolling rotational speed. Therefore, for example, in the outboard engine or the like which does not have a starter motor and is manually started, the foregoing method by the timer cannot be used. After the start of the engine, the ignition timing is soon returned to the timing in the stationary state. Therefore, there is a problem in that the rotation durability after the start of the engine when the engine is cold deteriorates.
Further, according to the method whereby the ignition timing and the engine speed are interlocked, even in the case of promptly accelerating, the ignition timing is advanced only after the engine speed actually increases, so that the accelerating performance cannot be generally improved.
Further, according to this method, the ignition timing is not delayed unless and until the engine speed actually decreases at the time of deceleration. Therefore, the decelerating performance is bad and there is also a case where the rotational speed does not decrease at all.